OF THE ANTWERP CRAG. 405 
developed branchial plate. Terminal lobes of first maxille short and thick. Branchial 
plate large and ovate, setose, and with four long deflexed sete at base. Feet elongated, 
with long, slender claws. Abdomen ending in a large acuminate process; post-abdo- 
minal lobes narrow, and bearing three hairs. Eyes mostly absent. 
BYTHOCYTHERE CONSTRICTA, Sars. 
Bythocythere constricta, G. O. Sars, Oversigt af Norges marine Ostrac. p. 85 ; Brady, Monog. Recent 
Brit. Ostr. p. 451, pl. xxxv. figs. 47-52; Brady, Crosskey, and Robertson, Monog. Post-tertiary 
Entom. Scotland, &c., p. 208, pl. xvi. figs. 9, 10. 
Carapace, as seen from the side, rhomboidal; height nearly equal throughout, and 
exceeding half the length; anterior extremity obliquely rounded; posterior obliquely 
truncate, rounded off at its upper angle; dorsal margin straight, ventral slightly sinuated 
near the middle, convex and inclined upwards behind. Seen from above, lozenge-shaped, 
distinctly constricted in the middle. Surface marked with delicate grooves running 
mostly in a subconcentric manner, but frequently anastomosing so as to form an irre- 
gular reticulation; lateral protuberance rounded and not very prominent; centre of the 
valves marked by a deep and wide transverse furrow. Length 35 inch (0°80 millim.). 
One imperfect specimen only was found, in the Sables moyens (zone a Bryozoaires) ; 
I have therefore been unable to give figures, and have drawn up the description from 
Scottish Post-tertiary specimens. B. constricta occurs in the living state on the coasts 
of Norway and the British Islands, usually in depths exceeding 10 fathoms. 
Genus CYTHERIDEIS, Jones. 
Carapace elongated, subovate, depressed in front; hinge-margins nearly simple; 
shell smooth, punctate, or sometimes grooved ; right valve overlapping the left in the 
centre of the ventral surface. Superior antenne slender, sparingly setose; last joint 
short and bearing six short terminal sete. Mandible slender and curved, with about 
four very small indistinct teeth: palp 4-jointed, its first joint bearing a conical tooth-like 
process; third joint bearing a comb-like series of straight, equal setze, in other respects 
like that of Cythere. First segment of the maxillz much stouter than the rest. 
CYTHERIDEIS (?) LITHODOMOIDES (Bosquet). (Plate LXIII. figs. 2 a2 d.) 
Bairdia lithodomoides, Bosquet, Entom. foss. terr. Tertiair. France, &c., p. 36, pl. ii. figs. 3a—d. 
Carapace, as seen from the side, oblong ovate, compressed, greatest height situated 
behind the middle and equal to scarcely half the length, depressed and rounded off in 
front, wider behind; dorsal margin gently arched, ventral straight or slightly sinuated. 
Seen from above, regularly ovate, compressed, widest behind the middle, pointed in front, 
rounded behind, width equal to the height. End view subcircular. Surface smooth, 
marked on the anterior portion of the shell with a number of shallow concentric grooves. 
Length 3g inch (0°98 millim.). 
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